This invention relates generally to power electronics, and more particularly to a power supply unit for providing backup power to a server and/or to other critical electrical equipment.
Organizations often employ data centers to manage their data processing and other computing needs. A data center typically houses many racks of servers, which together perform the processing tasks that a single machine could not. The role of a data center is often critical to an organization, and downtime of a data center can result in severe consequences to the organization and to others who may rely on the data center. Since power failures are not uncommon, data centers use power backup systems to deal with interruptions in the supply of power from utility services that would otherwise result in downtime.
One power backup system designed to provide emergency power to computing resources is called an uninterrupted power supply (UPS). In a typically data center deployment, a UPS is placed between the input power terminal from a utility service and one or more power distribution units in the data center, to which the servers are connected. When the utility power is functioning properly, the UPS uses a portion of the utility power to charge a battery within the UPS, using an internal rectifier to convert the AC power from the utility service into DC power for charging the battery. The majority of the remaining power from the utility service is passed along for use by the site. If an interruption in the utility power occurs, the UPS provides temporary backup power to the site by using an inverter to convert the DC power stored in its battery into AC power. This temporary power is available for a short period of time, allowing an auxiliary power supply (such as a generator) to be turned on or allowing the equipment to be shut down safely, thereby avoiding catastrophic loss.
Because the power conversions performed by the rectifiers and inverters in the UPS are relatively inefficient, the UPS process can result in a power loss of up to 10-12%. For large data centers, this inefficiency can be very significant. Not only is this a waste of electrical power and the costs associated therewith, it also produces heat at the UPS and thus requires additional electrical power to remove the additional heat using an air conditioning system. It would be desirable, therefore, to eliminate the need for the UPS system altogether, while still providing backup power to critical electrical equipment.
One alternative to a UPS is to place a backup battery on each motherboard in a data center. Although the backup batteries can supply power in the event of a utility power failure, this design suffers from a number of drawbacks. For example, locating the batteries on the motherboard increases the cooling requirements for the server, since the batteries must be kept away from higher temperatures. The design also requires a large number of batteries, one for each server motherboard, which increases the maintenance costs and as well as the monitoring requirements to ensure that the backup power system is reliable. Finally, given the large number of batteries, failure of at least some of the batteries is more likely, but this design provides no redundancy in the case of battery failure.